Sometimes I saw posts where the embedded images only show up when logged in. Now it happend to my own post: https://www.lfs.net/forum/thread/89251



I think it happens if you attach/upload the image but then write the text 'elsewhere.'
(For example click "Create New Thread" again in another browser tab. Or you notice you were about to post in wrong subforum and copy-paste your text)

Test:

^-- this picture only shows when logged in

1) upload image
2) get link to image ( https://www.lfs.net/attachment/137911 )
3) close forum
4) create a posting with the image.
5) Image works but only when logged in (?)

Hm ok, it's because attachments that are uploaded are linked to the reply page you are on. Going to another page discards the attachments and the attachments will not be tied to your new post.
That ties in with some attachment permission thing where demo users cannot download attachments that aren't used in posts (those because private attachments, although you cannot browse them - it's a kind of forgotten idea).

Anyway long story short ... I'm not actually sure how to fix this. It's kind of a bug, but not really. Basically you should try to upload images on the page you are actually going to submit the reply on. Then it will work. But I've made it so that images can always be viewed, for the time being anyway.